Diode keying system for electronic organ

ABSTRACT

The keying networks between continuously running square wave tone signal sources and the sound output system of an electronic organ each consist of an isolating diode gate for each source, followed by the parallel combination of at least two keying diode gates of simplified circuitry which either gate-through the square wave signal without change in wave shape (for odd-orderharmonic tones) or gate-through and modify the wave-shape into sawtooths (for full harmonic tones). A keyed activating circuit for the isolating diode gate and the keying diode gates corresponding to a selected key may contain a single key switch connected to a source of direct current and a common R-C attack network for two adjacent footage keying diode gates as well as for the paralleled keying diode gates. A common coupler switch for coupling between keyboards is located between the direct current source and auxiliary key switches ganged respectively to the main key switches for a given manual, the auxiliary key switches being connected to a diode to isolate them from the main key switches in the coupled keyboard.

United States Patent 72] Inventor Dale M. Uetrecht Cincinnati, Ohio [21]Appl. No. 755,043

[22] Filed Aug. 26, 1968 [45] Patented May 25, 1971 [73] Assignee D. H.Baldwin Company Cincinnati, Ohio [54] DIODE KEYING SYSTEM FOR ELECTRONICPrimary Examiner-Herman Karl Saalbach Assistant Examiner-SaxfieldChatmon, Jr. Attorney-W. H. Breunig ABSTRACT: The keying networksbetween continuously running square wave tone signal sources and thesound output system of an electronic organ each consist of an isolatingdiode gate for each source, followed by the parallel combination of atleast two keying diode gates of simplified circuitry which eithergate-through the square wave signal without change in wave shape (forodd-order-harmonic tones) or gatethrough and modify the wave-shape intosawtooths (for full harmonic tones). A keyed activating circuit for theisolating diode gate and the keying diode gates corresponding to aselected key may contain a single key switch connected to a source ofdirect current and a common R-C attack network for two adjacent footagekeying diode gates as well as for the paralleled keying diode gates. Acommon coupler switch for coupling between keyboards is located betweenthe direct current source and auxiliary key switches ganged respectivelyto the main key switches for a given manual, the auxiliary key switchesbeing connected to a diode to isolate them from the main key switches inthe coupled keyboard,

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DIODE KEYING SYSTEM FOR ELECTRONIC ORGAN BACKGROUND OF THE INVENTION Aninherent disadvantage of the variable-resistance-keyswitch system forelectronic organs is that the large number of decks of key switchesrequired in large organs must be located between manual keyboards, wherelimited space is available. Also, there is no provision for scaling theattack and decay of tones throughout a gamut other than the rate atwhich the keys are depressed and released. Further, coupling betweenkeyboards is required. This necessitates that each manual have the samefootages and wave shapes available as the keyboard to which it iscoupled.

In general, this limits the tone color variety between keyboards.Therefore, the principal objects of this invention are (l) to obtain asimple gate arrangement to minimize the number of switch decks, (2) toobtain desirable attack and decay character, (3) to obtain simple andcomplete coupling and (4) to obtain a wide variety of tone colors, whilemaintaining the cost advantage of a key switch system. Another object isto utilize the economic advantage of a distributed filter system of tonecolor filters over a currently used active filter system in which fiveactive filters are required for a five-octave keyboard at approximatelytwice the cost of an RC distributed filter as disclosed in a copendingapplication Ser. No.

by which the signal may be coupled prior to signal collection points bymeans of DC switching. Therefore, the other ad-' vantages of adistributed filter system can be utilized without switching at about lcollector points.

Prior art relevant to the present invention consists principally of U.S.patents to:

George 2,483,823

Munch et al. 3,223,768

Munch et al. 3,321,567

Bissonette et al. Ser. No. 541,380. George disclosed a vacuum diodekeyingcircuit for an electronic musical instrument, which required aseparate bias source for the diode. The Munch et al. patents show how toself-bias a single or double, solid-state diode gate with the'aid of acoupling capacitor between the tone signal source and the gate, thelatter patent being a continuation-in-part of the former. The latterMunch et al. patent expands the teachings of the former with respect towave-shaping in a diode gate. The Bissonette et al. application will bediscussed hereinafter.

With this prior art as background, the various aspects of this inventionarose as solutions to three problems in developing a practical diodekeying system. First, since a diode gate is a nonlinear device, it isnecessary to isolate the gate of one tone signal frequency from the gateof another tone signal frequency to minimize intermodulation distortion.In some percussion" gating systems an appreciable amount ofintermodulation distortion is tolerated, or elaborate filtering isprovided to minimize output distortion. However, in a complete gatingsystem for an organ, it is necessary to reduce intermodulationdistortion to about 0.1 percent without resorting to the cost ofelaborate tone color filtering.

The second problem is leakthrough. This may be defined as the ratio ofoutput signal present when a gate is off compared with the output signalpresent when the gate in on. The general requirement for leakthrough is80 db. up to 8000 Hertz. Diodes are presently available with straycapacitance of the order of l pf., but it is desirable to use lower-costdiodes having approximately pf. stray capacitance. At 8000 Hertz a l pf.capacitor has an impedance of 20 megohms. Therefore, a l pf. diode wouldrequire a 2-kilohm ON impedance. This requires unrealistic gate currentto achieve low leakthrough. Therefore, it is necessary, except forlow-capacitance diodes,

between them to reduce leakthrough, but his disclosure was I that of asingle gate containing the two diodes and a bypass impcdance.

The third problem is to provide two basic wave shapes which can befiltered in the output system to obtain desired tone colors. One must bea square wave, having only oddorder harmonics and preferably l/namplitude, where n is the harmonic number. The second is an all-harmonicwave shape, again with 1/n amplitude. Usually a linear saw tooth is usedfor the all-harmonic wave, as it contains harmonics at l/n amplitude. Toobtain alinear saw tooth it is necessary to discharge a capacitor duringa small fraction of a cycle and allow it to charge from the keyed sourcefor the remainder of the cycle. However, since more components arerequired to obtain this wave shape, an alternate wave shape was analyzedand found to have essentially the same harmonic structure. The latterwave shape is achieved by clamping a capacitor at one potential for ahalf period of a square wave input and allowing the capacitor to chargetoward another potential for the remaining half period.

The referenced copending patent application of Bissonette et al.,entitled Electronic Organ Gating System, Ser. No. 541,380, filed Apr. 8,1966, now abandoned and assigned to the assignee of this application,sets fort a basic approach to the solution of the second of the aboveproblems. In the cited reference, use is made of a common isolatingdiode gate for each source of tone signal, followed by a double-diodekeying gate employed for each footage in a given keyboard. However, theteachings of Bissonette and Munch are silent on the subject ofintermodulation distortion. Also, no provision is taught for achievingmore than one wave form at the output of keying diode gates turned on bya single key switch. Furthermore, therewere no teachings as to couplingthe tone .color filters normally associated with one keyboard with thekey switches of another keyboard. Likewise no mention was made for thescaling of attack networks throughout a gamut.

SUMMARY OF THE INVENTION The isolating diode gate associated with eachtone signal source comprises a series diode having a stray capacitanceof the order of 10 pf. and a shunt capacitor of about 1000 pf.,providing 40 db. isolation. An additional 40 db. isolation is easilyobtained across each of the paralleled keying diode gates, whichcomprise each a second diode in series next to the isolating diode, thesecond diode being followed in series by a relatively high resistor towhich is connected a collector for'the other tone signals which may bedirected through other gates to a particular tone color filter in theoutput system. This collector,-in turn, is shunted to ground by arelatively-low resistor. Therefore, the common collector is isolatedfrom the nonlinearity of the'keying diode gate by virtue of therelatively high series output resistor of the gate, thereby minimizingintermodulation distortion. Forward biasing potential for both diodes isapplied at the junction between the second diode and the relatively highseries resistor via the series combination of a direct current potentialsource, a key switch, and R-C attack network and a resistor, the latterbeing connected to the junction. The R-C attack network comprises afurther series resistor followed by a shunt capacitor, the latter twocomponents being scaled throughout the gamut of the system to provideshorter attack for the higher notes and a longer one for the lowernotes. A common R-C attack network for. a given key switch controls theenvelope of the signals passing through several of the keying diodegates corresponding to that switch. (These networks are called attacknetworks," because the decay of the signals is relatively unimportant-solong as it is not too long or too abrupt-in view of the face thatreverberation of the organ tones in a playing environment-sub- BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 is a partially block, partiallyschematic diagram of a circuit'providing a single path fora tone signalfrom a source thereof through isolating and keying gates to an outputsystem, according to the invention.

FIG. 1a is a partially block, partially schematic diagram of analternative to a portion of the diagram of FIG. 1.

' FIG. 2 is adiagram similar to FIG. 1, except that the keying gate hasprovision for wave-shaping.

FIG. 3 is a graph illustrating wave forms present in the embodiment ofFIG. 2.

FIG. 4 is a partially block, partially schematic diagram of the parallelcombination of the keying diode gates of FIGS. 1 and 2, plus a keyingdiode gate for a percussive" signal, all being connected. between acommon signal source and separate tone color circuits to amplificationand transducing means.

FIG. 5 is a partially block, partially schematic diagram of circuitsproviding tone signal paths from two frequency-adjacent tone sources intwo adjacent octaves through gates to the output system of an electronicorgan in accordance with the invention.

FIGS. 60 and 6b together comprise a partially block, partially schematicdiagram of the signal path and keying circuits for five of the octavelyrelated sources of an exemplary organ.

FIG. 7 is a chart giving practical values for certain components in acomplete organ system derived from the teaching of FIGS. 5, 6a and 6b.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 a tone signal source2, preferably supplying positive-going square waves, such as may bederived from one stage of achain of frequency dividing flip-flops, isconnected to an isolating diode gate 4, comprising a series diode 6(preferably a low-cost solid-state one), and a shunt capacitor 8, thesource 2 and'capacitor 8 being grounded, as shown, to a common returnpath. The junction 10 of the diode 6 and capacitor 8 is connected to akeying diode gate 12 via a branch 14, indicating where additional keyingdiode gates (not shown) may be connected. The gate 12 comprises a seriesdiode 16, a relatively high, voltage-dropping series resistor 18 andanother resistor 20 connected at the junction 22 of the diode l6 andresistor I8. One end of a further resistor 24 is connected, if ,needed(for reasons discussed hereinafter),

between the junction 22 and a common return path as shown. Tolthe otherend of the resistor 20 is connected an R-C attack network 26 composed ofa series resistor 28 and a shunt capacitor 30. The branch 32 indicateswhere additional keying gates (not shown) may be connected. The resistor26 is connected via a key switch 34 to a source of direct currentpotential (not shown) having a positive terminal 36. A branch 38indicates where other attack networks (not shown) may be connected.

The output end of the resistor 18 is connected via branch 40 and branch42 to an output system 44, composed of a tone color filter TC astop-switch 45, branch 46, amplifier 48 and loudspeaker 50, all inseries. The speaker 50 is preferably of the rotary, Doppler-effect type.The branch 40 indicates where additional keying gates (not shown) may beconnected; the branches 42 and 46 show where connections may be made toadditional tone color filters (not shown). The branch 42 is shownconnected to a common return path via a relatively-low resistor 52 (thatis, relatively low compared with relatively high resistor 18). Practicalvalues are 100 kilohms for resistor 18 and l2 kilohms for resistor 52.

In operation, when the switch 34 is in the off position (as shown),positive-going square waves from the source 2 are blocked by the diodes6 and 16, and maximum isolation exists between the source 2 and theoutput system 44. When the switch 34 is turned on, the DC potential V+at 36 starts to charge the capacitor 30 via the resistor 28 in theattack network 26. As the DC potential across the capacitor 8 builds up,it is applied to the diodes 6 and 16 causing them to conduct via theresistor 20 and the source 2. As the conductivity of the diodesincreases, the square-wave signal passes through the diodes 6 and l6andon to the output system 44, where it is modified in tone color by thefilter TC and flows to the amplifier 48 and loudspeaker 50, when thetone-color switch 45 is closed. Obviously, the signal may be interruptedby opening the switch 45. When the key switch 34 is opened, the signalwill decay as the resistivity of the diodes6 and 16 increases. Thoseskilled in the art will realize that attack and decay rates of thesignal will be determined principally by the time constant of resistors20 and 28 and capacitor 30. The network 26 is called an attack network,as mentioned above, the decay rate being less critical because of themasking of the decay of a tone by reverberation in the usual environmentsurrounding the loudspeaker 50.

The shunt capacitor 8 offers a relatively low-impedance path relative tothe off-impedance of the diode 6, thus providing a shunt path forleakthrough from diode 6. However, the capacitor 8 is a relatively highimpedance compared with the on-resistance of the diodes 6 and 16. Thusthe on signal is not substantially bypassed by the capacitor 8. Theshunt resistor 24 is not essential to the operation of the keying diodegate 12, but it not only contributes to feed-through reduction, but,also, it may be utilized to vary the signal attack when the same attacknetwork is used for another keying gate, (as will be discussed morefully hereinafter).

In the diagram of FIG. la, the dashed-line block 49 represents analternative to the source 2 and gate 4 and comprises portions of anintegrated circuit. One flip-flop circuit 241 in a chain thereof has aconnection to a buffer amplifier 4a comprising an MOSFET having anoutput lead 51. A square wave is present at all times at 53, while onthe lead 51, there is a wave-shaped signal when keying current ispresent. No signal is present in absence of keying voltage. If thisconfiguration is used, the diode 16 of FIG. 1 will be reversed and thekeying voltage at 36 will be negative. Thus, it is not intended thatthis invention be limitedto a diode isolating gate. Any equivalentgateproviding the necessary isolation and operable by the keying voltagemay be used.

The circuit of FIG. 2 is similar to that of FIG. 1, except that (l) ashunt timing capacitor 54 replaces the resistor 24 and (2) tone colorfilter TC replaces TC In operation, however, the keying diode gate isreverse biased during the positive-going half of every cycle. Thus thewave shape of the signal at junction 22 is altered by the capacitor 54.Reference is made to the graph of FIG. 3 for an explanation of thechange in wave shape.

In FIG. 3 signal voltage is plotted against time. At time t, thepositive excursion 55 of the source signal increases abruptly to itsmaximum at Y, and remains there until time During this half cycle of thesquare wave, the voltage across the capacitor 54 rises exponentiallyforming a ramp, as at 56, (the time constant being determinedprincipally be the resistor 20 and capacitor 54) until time when thesquare wave drops abruptly back to zero voltage. If the capacitor 54where allowed to charge to a level v it would follow the curve, as at58, and approach v asymptotically. The dashed line 60 shows an extensionof a true sawtooth for the half cycle shown. For the remainder of theperiod, the voltage across the capacitor remains at zero. If the timeconstant of the circuit including the capacitor 54 and the totalresistance of the path through which it is charged, is made equal to theperiod of one cycle of the wave, the relative harmonic structure of themodified sawtooth is nearly the desired 1 In. Actually, the fundamentalis 1.28/n (where n=l the third harmonic is 1.04/n (where n=3) and therecord and higher harmonics are approximately l/n.

Thus, if the keying diode gates of FIG. 1 and FIG. 2 are paralleledfollowing a common isolating diode gate and a common attack network,square waves and sawtooths will be available from a single source, keyedby means of a single key switch. This combination is illustrated in FIG.4, wherein some of the elements similar to those of FIGS. 1 and 2 aresimilarly designated. In FIG. 4 the keying gates 12 and 12' have acommon input through the branch 14 from the common source 2 andisolating gate 4. Also, a common attack network 26 is connected tokeying gates 12 and 12 via branch 31 The outputs of the keying gates 12and 12 are directed, as shown, via TC, and TC,, respectively, tocollectors 46 and 61, amplifiers 48 and 63, and loudspeakers 50 and 65,respectively. In addition is provided a separate attack network 62 andkeying diode gate 64 for percussive" signals (i.e., signals having anabrupt attack and gradual decay). To achieve these characteristics ofpercussion, the sustain capacitor 66 will be larger than the capacitor30, while the resistor 68 will be smaller than resistor 28. The sustainisolating diode 70 prevents the decaying percussive signal from passingback through the keying gates 12 and l2,'thereby allowing a long-sustainpercussion signal and short-sustain nonpercussive signal. The signalfrom the gate 64 (similar to gate 12, except for omission of a resistorcorresponding to resistor 24 of gate 12) is passed by branch 72 (forother keying gates, not shown) and branch 74 (for other tone colorfilters, not shown) to tone color filter TC appropriate for a percussivevoice, as known in the art. The output of the filter TC may be switchedby stop tab switch 76 to the collector 46' for signals to be amplifiedby amplifier 63 and radiated preferably by the rotary loudspeaker 65. Arelatively-low resistor 80 provides the path to ground for the branch74. v

In operation, square wave signals form the source 2 of FIG. 4 areblocked by gates 4, 12, 12 and 64 until keyed on by switch 34. Thesignal passes through gates 12 and 12' respectively, as activated bycommon attack network 26 in a manner similar to that of FIGS. 1 and 2.At the same time, signal passes via branch 14'. to gate 64, which isactivated by +V via the same key switch 34 but the separate attacknetwork 62. The square wave signal passes through the gate 64 withoutalteration, except that it decays slowly when the switch 34 is opened.As mentioned above, both the direct current keying voltage and signalthrough the gate 64-arexblocked by diode 70 from passing though any pathexcept through resistor 82 which is sufficiently highto cause a gradualdecay. Thus in FIG. 4 is illustrated the basic circuitry for developinga complete organ system.

The problem of intermodulation distortion will be discussed inconjunction with FIG. 5, which shows square wave keying gates for twoconsecutive notes in two adjacent octaves of an exemplary instrument.This also teaches the means for obtaining adjacent footagessimultaneously from a common key switch. Referring to FIG. 5, sources Cand C are the lowest two octavely related sources, while sources C andC0, are respectively a semitone higher. Isolating gate 84 couples sourceC to keying gate 86, containing diode 85 and resistor 87, to thejunction of which is connected, via resistor 83, attack network 88,which in turn is connected by way of key switch 90 to a direct currentbus 92 supplied with direct current potential by a source 94 thereof.Further, attack network 88 has a connection via line 96 to a secondkeying gate 98 the input side of which is coupled, as shown, to source Cvia isolating gate 100. The keying gate 86 is shown having an outputconnection past branches 89 and 91 (the latter having a groundingresistor 93) to a tone color filter 8' TC, which, in turn, may beconnected via tab switch 102 to collector 103 for signal being passed toamplifier 104 and loudspeaker 106.'The keying gate 98 has an outputconnection past branch points to a further tone color filter 16 TC,which, in turn may be connected via tab switch 108 to collector 103 forsignals being passed to amplifier 104 and 106.

Those portions of the system of FIG. pertaining to simultaneouslyproducing 8 and 16' tones operate as follows. Closure of the key switch90 directs activating potential to the isolating gates 84 and 100 andkeying gates 86 and 98 by way of common attack network 88. The outputsof the keying gates 86 and 98 are filtered by filters 8 TC and 16 TC,respectively, and upon closure of tab switches 102 and 108,respectively, for amplification by amplifier 104 and loudspeaker 106.

Also, there is illustrated in FIG. 5 the circuitry for obtaining twoadjacent semitones. The circuitry for C has just been described. In asimilar manner the source C0 is connected via isolating gate 108 tokeying gate 110, containing diode 109 and resistor 111, which, in turn,is connected to collector 112 which has a connection to tone colorfilter 8' TC, where the path to loudspeaker 106 is the same as for theoutput of keying gate 86. The operation of the path of the signal fromC0 is similar to that of the path for C However, it is pointed out thatin the collector 112, there is the combination of nonharmonicallyrelated signals. This is a condition where intermodulation distortioncan become a problem. This intermodulation is kept at a minimum bymaking the value of the resistors 87 and 111 large compared to thecyclic variation of the impedance looking back therefrom through theirrespec-' tive pairs of gating diodes to the sources C and C0respectively. Also, the resistor 93 is made low compared with resistors87 and 111. The latter resistors may be of the order of I00 kilohms andthe resistor 93 about I to 2 kilohms. Keying gate resistors such as 83and 107 are preferably scaled small at higher frequencies to keep theleakthrough down and high at lower frequencies to keep wave-shapingcapacitors such as 54 (FIG. 2) at a convenient size. Also, by scalingresistors such as 83 and 107, the attack network capacitors such as 30(FIG. 4), may be the same value for a whole keyboard. It was found thatthe random variations in attack rate which resulted from +80 percent, 20percent electrolytic capacitors were not generally noted. These randomvariations blend in to an average effect.

In FIGS. 6a and 6b there is illustrated typical circuitry for fiveconsecutive C notes in an organ system, including interkeyboardcoupling, sharing of attack networks by adjacentfootage signals andsharing of isolating gates. The five corresponding sources are indicatedas C to C inclusive. To these sources are connected isolating diodes 6(indicia correspond to FIGS. 1 and 2), with capacitors 8 shunting them,as shown. From the junction of each capacitor 8 and diode 6, connectionis made to a branch 14' from which further connection is made to all thekeying diode gates for a given signal frequency, and being composed of aseries diode 16, series resistor R gating resistor R,, shunt resistor R,(or shunt capacitor 54). To R, is connected, as taught in precedingfigures an attack network composed of series resistor 28 and shuntcapacitor 30, except for the percussive gates, whose series resistorsare labeled 68 and whose capacitors are marked 66. The resistors 28 haveconnections respectively to key switches 34, which are actuable byplaying keys labeled C X, C X in one keyboard and C Y, C Y in anotherkeyboard. The attack resistors 68 (for percussive notes) are isolatedfrom their respective key switches 34 by diodes 70, respectively. Keys CY and C,Y have ganged thereto (along with switches 34), auxiliaryswitches 114, which have a common connection 116 to an interkeyboardcoupler switch 118, preferably actuated by a stop tab 120.

Continuing with FIGS. 6a and 6b, the input side of resistors R have thepreviously-mentioned grounded shunt resistors (corresponding to resistor24 in FIG. 1) K, respectively connected thereto. To the output side ofthe resistor R there is a first branch (for other parallel gates, notshown) and a second branch (for other tone color filters, not shown). Tothe second branch for each output lead is connected a tone color filtercorresponding to the TCs of FIG. 4. Each filter in FlGS..;6a and 6b isdesignated with the footage of the processed signal plus a block or atriangle, indicating whether the filter is for a square wave or asawtooth, respectively. Tab-operated stop switches such as thosedesignated 45, 59, and 76 are respectively the switches for square wave,sawtooth and percussion 46' to which are connected amplifier 48 androtary loudspeaker-50. The sawtooth wave filters are shown connected viaoutput collector 61 to amplifier 63 and stationary speaker 65.

in operation, the signals respectively are blocked by isolating diodegates each having components consisting of diode 6 and capacitor 8 andby the keying diode gates each having components such as diode 16 andresistors R,, R and R, (or capacitor 54, if for sawtooth signal).Activating direct current for both types of gates is provided by attacknetworks each composed of a resistor 28 and a capacitor 30, except forpercussion. The percussion signals are keyed-on through such attacknetworks as those composed of series resistor 68 and shunt capacitor 66.The isolating diodes 70 serve the same purpose as diode 70 in FIG. 4. Itwill be noted that a single key switch 34 (for key C X, for example)keys direct current from source 122 thereof to three attack networks124, 126 and 127. Network 124 activates keying gates 128, 130 and 132for 8' and 16v voices at "a relatively slower rate than does network 126activatekeying gates 134 and 136 for 4 and 2' voices. (it is, of course,characteristic of pipe organs that lower-pitched pipes in a given rankspeak more slowly than higher-pitched pipes). A still more abrupt attackis preferably provided by attack network 127 for percussive voices, viakeying gates 138 and 140. It can be seen that a single attack networkcan be comprised to provide acceptable rise time for tone signals ofadjacent footages. it can also be seen that tracing signal paths keyedby key C X (an octave higher than C X) that output signals will pass tothe same filters as those for C X.

The signal and DC paths for keys C Y and C Y (in a keyboard Y) are shownas similar in arrangement and operation to those for-C X and C X, exceptthat no percussion is provided. However, the previously-mentionedcoupler switch 118, if closed, makes direct current available throughauxiliary switches 114, so-that direct current corresponding to notesplayed on the Y keyboard will be directed, for example, via diode 141and lead 142 to the same attack networks 124, 126 and 127 which arenormally effective when C X is depressed. Thus isprovided a simpleone-switch coupler arrangement. The diode 141 obviously isolates keyswitches 114 from key switches 34 in'the reverse direction.

In FIG. 7 are given the scaled values for R,,, R, and capacitor 54in thesystem of FIGS. 6a' and 6b. For example, the capacitor 54 is 0.12 mf.vin the sawtooth keying gates for lowest three notes (C, CO and D) ofthe first (lowest) octave in the gamut. The next higher three notes (D0,E and F) use a 0.10 mi. capacitor 54. The signals for the highest octaveare from the master oscillators in a frequency-divider chain offlip-flops previously mentioned and no capacitors 54 are needed, sincemost of the harmonics are available in the master oscillator wave form.

As has been previously mentioned, use of low-cost l pf. diodesnecessitates two diodes in series to obtain the desired leakthroughisolation. It has been shown how a single diode on each source outputcan be shared by as many keying gate diodes as desired, so long as otherleakthrough requirements are met. When no gates are operated in their oncondition, the isolating diode provides 40 db. isolation by means of thecapacitor divider (that is, the pf. stray capacitance of the diodeshunted by a 1,000 pf. capacitor). An additional 40 db. isolation iseasily obtained across the keying gate diode. However, when the sharedisolating diode gate is operated by one keying gate, the 40 db.isolation is lost with respect to a parallel keying gate which is noton. The isolation of this keying gate must then be able to take care ofsneak paths. One such path occurs when a subharmonic signal is gated onat a lower footage that is not stop-tabbed and leaks across the keyinggate in a lower octave of the footage that is stop-tabbed. Anotherpossible sneak path occurs when an isolating diode is turned on from onekeyboard at a frequency not tabbed and leaks across the keying gate of asecond keyboard where that frequency is tabbed. Therefore an isolationbetween 40 and 60 db. is required for the keying gate, or an impedanceof from 2 to 20 kilohms at 8,000 Hertz when 10 pf. diodes are used. Theactual impedances were sealed down to 15K at 8,000 Hertz to maintainreasonable keying currents, and 1 pf. diodes were used in a few caseswhere additional isolation was required.

Thus the primary objective of obtaining a simple, and thereforeeconomical gating system has been accomplished. As a result of using agating system, controlled attack and direct coupling is obtained. Inaddition to simplicity, a significant virtue of the gate of the presentinvention is that two desirable wave shapes can be obtained. As a directresult of the wave shapes available, and the direct coupling, a widevariety of quality tone colors can be obtained using the simpledistributed filters previously mentioned. v

For the purposes of the claims, a keying network comprises an isolatinggate, one or more keying gates connected in parallel thereto, anattack-network with associated key switch and direct current source.Anfactivating circuit is composed of an attack network, a key switch anda direct current source.

Although this specification includes isolating gates for each source, sothat higher-stray-capacitance, low-cost diodes can be used, it will beobvious to one skilled in the art that highercost,lower-stray-capacitance diodes may obviate the necessity of isolatinggates. This does not detract fromthe utility of the keying gates of thepresent application which in themselves are believed new and useful inthe art for the purposes described.

While 1 have described and illustrated specific embodiments of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What 1 claim is:

1. An electronic music system having in cascade a continuous tone signalsource, a keying network and an output system, said keying networkcomprising in combination:

an isolating gate coupled tosaid signal source,

a first and a second keying gate in parallel between said isolating gateand said output system, saidsecond keying gate having wave-shapingcharacteristics different from those of said first keying gate, and

a common activating circuit. for both said gates respectively coupled tosaid first and said second keying gates.

2. The combination according to claim 1 wherein said activating circuitincludes in cascade with a source of direct current potential:

a key switch and I a first R-C attack network coupled respectivelyto-said first and said second keying gates.

3. The combination according to claim 2 wherein said signal sourcesupplies square waves, wherein said first keying gate is arranged andadapted to pass said square waves substantially without change in shape,wherein said second keying gate is arranged and adapted to shape saidsquare waves substantially into sawtooth waves and wherein said outputsystem includes:

a first tone color filter coupled to said first keying gate and g asecond tone color filter coupled to said second keying gate.

4. The combination according to claim 2 including:

a third keying gate in parallel with said first and said second keyinggate between said isolating gate and said output system, and

a second R-C attack network coupled between said key switch and saidthird keying gate.

5. The combination according to claim 3 wherein said first keying gatecomprises the combination of:

a first diode coupled to said isolating gate,

a first relatively high resistor in series with said first diode andsaid first tone color filter,

a second relatively-low resistor shunted between a common return pathand the junction between said first resistor and said first tone colorfilter, said relatively-low resistor being of the order of twomagnitudes lower than said relatively high resistor; and' a thirdvoltage-dropping resistor between said first attack network and thejunction between said first diode and said first resistor.

6. The combination according to claim 3 wherein said second keying gatecomprises the combination of:

a first diode coupled to said isolating gate,

a first relatively high resistor in series with said first diode andsaid second tone color filter,

a capacitor shunted between a common return path and the junctionbetween said first diode and said first resistor,

a second voltage-dropping resistor between said junction and said firstattack network and a third relatively-low resistor shunted between thecommon return path and the junction between said first resistor and saidsecond tone color filter, said relatively-low resistor being of theorder of two magnitudes lower than saidrelatively high resistor.

7. The combination according to claim 4 wherein said signal sourcesupplies square waves, wherein said first keying gate passes said squarewaves substantially without change in shape, wherein saidsecond keyinggate shapes said square waves substantiallyinto sawtooths, wherein saidthird keying gate passes said square waves substantially without changeand wherein said output system includes:

a first tone color filter for square waves coupled to said first keyinggate,

a second tone color filter for sawtooths coupled to said second dyeinggate and a third percussive tone color filter coupled to said thirdkeying gate;

8. The combination according to 'claim 4 wherein a first diode iscoupled between said key switch and said second R-C attack network andwherein said third keying gate comprises the combination of:

a second diode coupled to said isolating gate,

a first relatively high resistor between saicl second diode and saidoutput system,

a second voltage-dropping resistor between said second R-C attacknetwork and the junction between said second diode and said firstresistor and:

a third relatively-low resistor shunted between the common return pathand the junction between said first resistor and said output system,saidrelatively-low resistor being of the order of two magnitudes lowerthan said relatively high resistor.

9. The combination according to claim 7 wherein said first keying gatecomprises the combination of:

a first diode coupled to said isolating gate,

a first relatively high resistor between said first diode and said firsttone color filter,

a second relatively low resistor shunted between a common return pathand the junction between said first resistor and said first tone colorfilter, said relatively low resistor being of the order of twomagnitudes lower than said relatively high resistor,

a third voltage-dropping resistor between said first attack network andthe junction between said first diode and said.first resistor, whereinsaidsecond keying gate comprises the combination of:

a second diode coupled to said isolating gate,

a fourth relatively high resistor in series with said second diode andsaid tone color filter,

a capacitor shunted between said common return path and the junctionbetween said second diode and said fourth resistor; and

a fifth resistor between said last-mentioned junction and said first R-Cattack network, and wherein a third diode is coupled between'said keyswitch and said second R-C attack network and wherein said third diodekeying gate comprises the combination of:

a fourth diode coupled to said isolating gate,

a sixth relatively high resistor between said fourth diode and saidthird tone color filter,

'a seventh resistor between said second R-C attack network and thejunction between said fourth diode and said sixth resistor,

an eighth resistor between said last-mentioned junction and said commonreturn path and a ninth relatively low resistor shunted between thecommon return path and the junction between said sixth resistor and saidthird tone color filter, said ninth relatively low resistor being of theorder of two magnitudes lower than said sixth relatively high resistor.

10. An electronic music system having a first continuous tone signalsource, a second continuous tone source, an output system, a firstkeying network between said 'firsttone signal source andsaid outputsystem, and a second keying network between said second tone signalsource and said output system, said keying networks each comprising:

an isolating gate coupled to its corresponding tone signal source,

a first keying gate coupled between said isolating gate and said outputsystem, and w an activating circuit for the gates in each of said keyingnetworks, each first keying gate comprising:

a first diode and a first relatively high resistor in series between itscorrespohding isolating gate and said output system,

a second voltage-dropping resistor between said common activatingcircuit and a first junction between said diode and said first resistorand a third relatively low resistor shunted between a common return pathand a second junction between said first resistor and said outputsystem, said relatively low resistor being of the order of twomagnitudes lower than said relatively high resistor,

wherein said keying networks each include a second keying gate inparallel with said first keying gate, each second keying gatecomprising;

a second diode and a fourth relatively high resistor in series betweenits corresponding isolating gate and said output system,

a fifth voltage-dropping resistor between said common activating circuitand said first junction,

a capacitor coupled between said common return path and said firstjunction,

and a sixth relatively low resistor between said common return path andsaid second junction, said relatively-low resistor being of the order oftwo magnitudes lower than said relatively high resistor.

11. In an electronic music system, the combination comprising:

a continuous tone signal source,

an isolating gate coupled thereto,

an output system,

four keying gates in parallel between the isolating gate and the outputsystem, the first of the keying gates having different wave-shapingcharacteristics from the second of the keying gates, the third of thekeying gates having correspondingly different wave-shapingcharacteristics from the fourth of the keying gates,

a first common activating circuit for the isolating gate and for thefirst and second keying gates respectively coupled to the first andsecond keying gates and a second common activating circuit for theisolating gate and for the third and fourth keying gates respectivelycoupled to the third and fourth keying gates.

12. The combination according to claim 11, wherein. each oftheactivating circuits include in cascade:

a common source of direct current potential,

a key switchand an R-C attack network coupled to the keying gatescorrespondingthereto.

13." The combination according to claim 11, wherein the tone signalsource supplies square waves, wherein the first and third keying gatespass the square waves substantially without change in shape, wherein thesecond and fourth keying gates shape the square wave substantially intosawtooths and wherein the output system includes:

a'first tone color filter coupled to the first and third keying gatesand v a secorid tone color filter coupled to the second and fourthkeying gates.

14. The combination according to claim 13, wherein the R-C attacknetworks have different characteristics.

' 15. The combination according to claim 13, wherein the key switch inthe first of the activating circuits corresponds to a key in a firstkeyboard and the key switch in the second of the activating circuitscorresponds to a key in a second keyboard. i I 7 16. The combinationaccording to claim 13, wherein said first and third keyinggates eachcomprise the combination of:

a first diode coupled to the isolating gate,

a first relatively high resistor in series with the and the first tonecolor filter,

a second relatively low resistor shunted between a common return pathand the junction between the first resistor and the first tone colorfilter, said relatively low resistor being of theorder of two magnitudeslower than said relatively high resistor,

a third resistor between the attack network in the first activatingcircuit and the junction between the'first diode and the'first resistor.r

17. The combination according to claim 13, wherein the second and fourthkeying gates each comprise the combination of:

a first diode coupled to the isolating gate,

a first relativelyhigh resistor in series'with the first diode and thesecond tone color filter,

a capacitor shunted between a common return path and the junctionbetween the first diode and the first resistor, a secondvoltage-dropping resistor between the junction and the second attacknetwork and a third relatively low resistor. shunted between the commonreturn path and the junction between the first resistor and i the secondtone color filter, said relatively low resistor being of the order oftwo magnitudes lower than said relatively high resistor.

' 18. The combination according to claim 15, including:

a third key switch ganged to the key switch in the first of thactivating circuits, I

a coupler switch connected between the source of direct currentpotential and the third key switch.

19. The combination according to claim 18, including:

a first diode between the third key switch and the first of theactivating circuits.

20. In an electronic organ, the combination comprising:

a gamut of tone signal sources,

a plurality of isolating gates respectively coupled to said signalsources,

a plurality of keying gate groups, each plural group comprising gatescoupled in parallel to each of said isolating gates, said keying gatesof a group having different wave shaping characteristics one from theother,

a plurality of activating circuits each circuit coupled to controlconduction through a different group of said keying gates, and

an output system coupled to said keying gates.

21. The combination according to claim 20 wherein each activatingcircuit includes in cascade with a source of direct currentpotential:

a key switch and a first R-C attack network coupledto said at least twokeying gates.

22. The combination according to claim 21 wherein said signal sourcessupply square waves, wherein the first of said at first diode least twokeying gates passes square waves substantially without change in shape,wherein the second of said at least two keying gates shapes said squarewaves substantially into sawtooths and wherein said output systemincludes:

a first tone color filter coupled to all said first keying gates of saidfirst keying gates comprises the combination of:

a first diode'coupled to its corresponding isolating gate, a firstrelatively high resistor in series with said first diode and said firsttone color filter, r a second relatively low resistor shunted between acommon return path and the junction between said first resistor and saidfirst tone color filter, said relatively low resistor being of the orderof two magnitudes lower than said relatively high resistor, and a 25 athird voltage-dropping resistor between said first attack network andthe junction between said first diode and said first resistor.

25. The combination according to claim 22, wherein each of said secondkeying gates comprises the combination of:

a first diode coupled to its corresponding isolating gate,

a first relatively high resistor in series with said first diode andsaid second tone colorfilter,

a capacitor shunted between a common return path and the junctionbetween said first diode and said first resistor,

a second voltage-dropping resistor between said junction and said firstattack network, and

a third relatively low resistor shunted between the common return pathand the junction between said first resistor and said second tone colorfilter, said relativelylow resistor being of the order of two magnitudeslower than said relatively high resistor.

26. The combination according to claim '23 wherein said signal sourcessupply square waves, wherein each of said first keying gates pass saidsquare waves substantially without change in shape, wherein eachof saidsecond keying gates shapes said square waves substantially intosawtooths, wherein each of said third keying gates passes said'squarewaves substantially without change and wherein said output systemincludes: i

a first tone color filter for square waves coupled to said first keyingdiode gates,

a second tone color filter for sawtooths coupled to said a third tonecolor filter for percussion coupled to said third keying gates.

27. The combination according to claim 23 wherein a first diode iscoupled between each of said key switches and each of said second R-Cattack networks and wherein each of said third keying gates comprisesthe combination of:

60 a second diode coupled to its corresponding isolating gate,

a first relatively high resistor between said second diode and saidoutput system,

a second voltage-dropping resistor between said second R-C attacknetwork and the junction between said second diode and said firstresistor,

a third relatively low resistor shunted between the common return pathand the junction between said first resistor and said output system,said relatively low resistor being of the order of two magnitudes lowerthan said relatively high resistor.

28. The combination according to claim 26 wherein each of said firstkeying gates comprises the combination of:

a first diode coupled to its corresponding isolating gate,

a first relatively high resistor between said first diode and said firsttone color filters,

a second relatively low resistor shunted between a common return pathand the junction between said first resistor and said first tone colorfilter, said relatively low resistor being of the order of twomagnitudes lower than said relatively high resistor,

a third voltage-dropping resistor between said first attack network andthe junction between said first diode and said first resistor, whereineach of said second gates comprises the combination of:

a second diode coupled to its corresponding isolating gate,

a fourth relatively high resistor in series with said second diode andsaid tone color filter,

a capacitor shunted between said common return path and the junctionbetween said second diode and said fourth resistor, and

a fifth voltage-dropping resistor between said last-mentioned junctionand said first R attack network, wherein a third diode is coupledbetween said key switch and said second R-C attack network and whereineach of said third keying gates comprises the combination of a fourthdiode coupled to its corresponding isolating gate,

a sixth relatively high resistor between said fourth diode and saidthird tone color filter,

a seventh voltage-dropping resistor between said second R-C attacknetwork and the junction between said fourth diode and said sixthresistor,

an eighth resistor between said last-mentioned junction and said commonreturn path, and

a ninth relatively low resistor shunted between thecommon return pathand the junction between said sixth resistor and said third tone colorfilter, said ninth relatively-low resistor being of the order of twomagnitudes lower than said sixth relatively high resistor.

29. In an electronic organ,

a source of periodic square wave tone signals which alternate between afirst and a reference level,

a single isolating gate, which is nonconductive of signals whenunbiased, connected in cascade with said source,

a plurality of solid-state electronic keying gates connected in parallelwith each other and all connected in series with said single isolatinggate,

a single key operated switch for applying DC bias voltage concurrentlythrough all said gates and through said source to a reference point, and

different circuits connected between said kcy operated switch and eachseparate one of said keying gates, one of said different circuits beingresponsive to said square wave signals for generating correspondinglyshaped square waves, and

another of said different circuits being responsive to said square wavesignals for generating periodic ramp waves, and

still another of said different circuits including a percussive sustaincircuit connected between said single key operated switch and one ofsaid keying gates.

30. The combination according to claim 29 wherein said single isolatinggate is a solid-state switch having an output terminal, said solid-stateswitch presenting a leakage capacity C in series with said sources, anda capacitor of value nC shunting said output terminal to a referencelevel, where n is of the order of 100.

31. The combination according to claim 29 wherein said single isolatinggate is a solid-state diode having an output terminal, said solid-statediode having a leakage capacity C in series with said source and acapacitor of value nC shunting said output terminal to a referencelevel, where n is of the order of 100.

32. The combination according to claim 29 wherein all said gates aresolid-state gates.

1. An electronic music system having in cascade a continuous tone signalsource, a keying network and an output system, said keying networkcomprising in combination: an isolating gate coupled to said signalsource, a first and a second keying gate in parallel between saidisolating gate and said output system, said second keying gate havingwave-shaping characteristics different from those of said first keyinggate, and a common activating circuit for both said gates respectivelycoupled to said first and said second keying gates.
 2. The combinationaccording to claim 1 wherein said activating circuit includes in cascadewith a source of direct current potential: a key switch and a first R-Cattack network coupled respectively to said first and said second keyinggates.
 3. The combination according to claim 2 wherein said signalsource supplies square waves, wherein said first keying gate is arrangedand adapted to pass said square waves substantially without change inshape, wherein said second keying gate is arranged and adapted to shapesaid square waves substantially into sawtooth waves aNd wherein saidoutput system includes: a first tone color filter coupled to said firstkeying gate and a second tone color filter coupled to said second keyinggate.
 4. The combination according to claim 2 including: a third keyinggate in parallel with said first and said second keying gate betweensaid isolating gate and said output system, and a second R-C attacknetwork coupled between said key switch and said third keying gate. 5.The combination according to claim 3 wherein said first keying gatecomprises the combination of: a first diode coupled to said isolatinggate, a first relatively high resistor in series with said first diodeand said first tone color filter, a second relatively-low resistorshunted between a common return path and the junction between said firstresistor and said first tone color filter, said relatively-low resistorbeing of the order of two magnitudes lower than said relatively highresistor; and a third voltage-dropping resistor between said firstattack network and the junction between said first diode and said firstresistor.
 6. The combination according to claim 3 wherein said secondkeying gate comprises the combination of: a first diode coupled to saidisolating gate, a first relatively high resistor in series with saidfirst diode and said second tone color filter, a capacitor shuntedbetween a common return path and the junction between said first diodeand said first resistor, a second voltage-dropping resistor between saidjunction and said first attack network and a third relatively-lowresistor shunted between the common return path and the junction betweensaid first resistor and said second tone color filter, saidrelatively-low resistor being of the order of two magnitudes lower thansaid relatively high resistor.
 7. The combination according to claim 4wherein said signal source supplies square waves, wherein said firstkeying gate passes said square waves substantially without change inshape, wherein said second keying gate shapes said square wavessubstantially into sawtooths, wherein said third keying gate passes saidsquare waves substantially without change and wherein said output systemincludes: a first tone color filter for square waves coupled to saidfirst keying gate, a second tone color filter for sawtooths coupled tosaid second dyeing gate and a third percussive tone color filter coupledto said third keying gate.
 8. The combination according to claim 4wherein a first diode is coupled between said key switch and said secondR-C attack network and wherein said third keying gate comprises thecombination of: a second diode coupled to said isolating gate, a firstrelatively high resistor between said second diode and said outputsystem, a second voltage-dropping resistor between said second R-Cattack network and the junction between said second diode and said firstresistor and a third relatively-low resistor shunted between the commonreturn path and the junction between said first resistor and said outputsystem, said relatively-low resistor being of the order of twomagnitudes lower than said relatively high resistor.
 9. The combinationaccording to claim 7 wherein said first keying gate comprises thecombination of: a first diode coupled to said isolating gate, a firstrelatively high resistor between said first diode and said first tonecolor filter, a second relatively low resistor shunted between a commonreturn path and the junction between said first resistor and said firsttone color filter, said relatively low resistor being of the order oftwo magnitudes lower than said relatively high resistor, a thirdvoltage-dropping resistor between said first attack network and thejunction between said first diode and said first resistor, wherein saidsecond keying gate comprises the combination of: a second diode coupledto said isolating gate, a foUrth relatively high resistor in series withsaid second diode and said tone color filter, a capacitor shuntedbetween said common return path and the junction between said seconddiode and said fourth resistor; and a fifth resistor between saidlast-mentioned junction and said first R-C attack network, and wherein athird diode is coupled between said key switch and said second R-Cattack network and wherein said third diode keying gate comprises thecombination of: a fourth diode coupled to said isolating gate, a sixthrelatively high resistor between said fourth diode and said third tonecolor filter, a seventh resistor between said second R-C attack networkand the junction between said fourth diode and said sixth resistor, aneighth resistor between said last-mentioned junction and said commonreturn path and a ninth relatively low resistor shunted between thecommon return path and the junction between said sixth resistor and saidthird tone color filter, said ninth relatively low resistor being of theorder of two magnitudes lower than said sixth relatively high resistor.10. An electronic music system having a first continuous tone signalsource, a second continuous tone source, an output system, a firstkeying network between said first tone signal source and said outputsystem, and a second keying network between said second tone signalsource and said output system, said keying networks each comprising: anisolating gate coupled to its corresponding tone signal source, a firstkeying gate coupled between said isolating gate and said output system,and an activating circuit for the gates in each of said keying networks,each first keying gate comprising: a first diode and a first relativelyhigh resistor in series between its corresponding isolating gate andsaid output system, a second voltage-dropping resistor between saidcommon activating circuit and a first junction between said diode andsaid first resistor and a third relatively low resistor shunted betweena common return path and a second junction between said first resistorand said output system, said relatively low resistor being of the orderof two magnitudes lower than said relatively high resistor, wherein saidkeying networks each include a second keying gate in parallel with saidfirst keying gate, each second keying gate comprising: a second diodeand a fourth relatively high resistor in series between itscorresponding isolating gate and said output system, a fifthvoltage-dropping resistor between said common activating circuit andsaid first junction, a capacitor coupled between said common return pathand said first junction, and a sixth relatively low resistor betweensaid common return path and said second junction, said relatively-lowresistor being of the order of two magnitudes lower than said relativelyhigh resistor.
 11. In an electronic music system, the combinationcomprising: a continuous tone signal source, an isolating gate coupledthereto, an output system, four keying gates in parallel between theisolating gate and the output system, the first of the keying gateshaving different wave-shaping characteristics from the second of thekeying gates, the third of the keying gates having correspondinglydifferent wave-shaping characteristics from the fourth of the keyinggates, a first common activating circuit for the isolating gate and forthe first and second keying gates respectively coupled to the first andsecond keying gates and a second common activating circuit for theisolating gate and for the third and fourth keying gates respectivelycoupled to the third and fourth keying gates.
 12. The combinationaccording to claim 11, wherein each of the activating circuits includein cascade: a common source of direct current potential, a key switchand an R-C attack network coupled to the keying gates correspondingtHereto.
 13. The combination according to claim 11, wherein the tonesignal source supplies square waves, wherein the first and third keyinggates pass the square waves substantially without change in shape,wherein the second and fourth keying gates shape the square wavesubstantially into sawtooths and wherein the output system includes: afirst tone color filter coupled to the first and third keying gates anda second tone color filter coupled to the second and fourth keyinggates.
 14. The combination according to claim 13, wherein the R-C attacknetworks have different characteristics.
 15. The combination accordingto claim 13, wherein the key switch in the first of the activatingcircuits corresponds to a key in a first keyboard and the key switch inthe second of the activating circuits corresponds to a key in a secondkeyboard.
 16. The combination according to claim 13, wherein said firstand third keying gates each comprise the combination of: a first diodecoupled to the isolating gate, a first relatively high resistor inseries with the first diode and the first tone color filter, a secondrelatively low resistor shunted between a common return path and thejunction between the first resistor and the first tone color filter,said relatively low resistor being of the order of two magnitudes lowerthan said relatively high resistor, a third resistor between the attacknetwork in the first activating circuit and the junction between thefirst diode and the first resistor.
 17. The combination according toclaim 13, wherein the second and fourth keying gates each comprise thecombination of: a first diode coupled to the isolating gate, a firstrelatively high resistor in series with the first diode and the secondtone color filter, a capacitor shunted between a common return path andthe junction between the first diode and the first resistor, a secondvoltage-dropping resistor between the junction and the second attacknetwork and a third relatively low resistor shunted between the commonreturn path and the junction between the first resistor and the secondtone color filter, said relatively low resistor being of the order oftwo magnitudes lower than said relatively high resistor.
 18. Thecombination according to claim 15, including: a third key switch gangedto the key switch in the first of the activating circuits, a couplerswitch connected between the source of direct current potential and thethird key switch.
 19. The combination according to claim 18, including:a first diode between the third key switch and the first of theactivating circuits.
 20. In an electronic organ, the combinationcomprising: a gamut of tone signal sources, a plurality of isolatinggates respectively coupled to said signal sources, a plurality of keyinggate groups, each plural group comprising gates coupled in parallel toeach of said isolating gates, said keying gates of a group havingdifferent wave shaping characteristics one from the other, a pluralityof activating circuits each circuit coupled to control conductionthrough a different group of said keying gates, and an output systemcoupled to said keying gates.
 21. The combination according to claim 20wherein each activating circuit includes in cascade with a source ofdirect current potential: a key switch and a first R-C attack networkcoupled to said at least two keying gates.
 22. The combination accordingto claim 21 wherein said signal sources supply square waves, wherein thefirst of said at least two keying gates passes square wavessubstantially without change in shape, wherein the second of said atleast two keying gates shapes said square waves substantially intosawtooths and wherein said output system includes: a first tone colorfilter coupled to all said first keying gates and a second tone colorfilter coupled to all said second keyinG gates.
 23. The combinationaccording to claim 21 including: a plurality of third keying gates eachin parallel with said at least two keying gates and a plurality ofsecond R-C attack networks respectively coupled between each key switchand each of said third keying gates.
 24. The combination according toclaim 22, wherein each of said first keying gates comprises thecombination of: a first diode coupled to its corresponding isolatinggate, a first relatively high resistor in series with said first diodeand said first tone color filter, a second relatively low resistorshunted between a common return path and the junction between said firstresistor and said first tone color filter, said relatively low resistorbeing of the order of two magnitudes lower than said relatively highresistor, and a third voltage-dropping resistor between said firstattack network and the junction between said first diode and said firstresistor.
 25. The combination according to claim 22, wherein each ofsaid second keying gates comprises the combination of: a first diodecoupled to its corresponding isolating gate, a first relatively highresistor in series with said first diode and said second tone colorfilter, a capacitor shunted between a common return path and thejunction between said first diode and said first resistor, a secondvoltage-dropping resistor between said junction and said first attacknetwork, and a third relatively low resistor shunted between the commonreturn path and the junction between said first resistor and said secondtone color filter, said relatively low resistor being of the order oftwo magnitudes lower than said relatively high resistor.
 26. Thecombination according to claim 23 wherein said signal sources supplysquare waves, wherein each of said first keying gates pass said squarewaves substantially without change in shape, wherein each of said secondkeying gates shapes said square waves substantially into sawtooths,wherein each of said third keying gates passes said square wavessubstantially without change and wherein said output system includes: afirst tone color filter for square waves coupled to said first keyingdiode gates, a second tone color filter for sawtooths coupled to said athird tone color filter for percussion coupled to said third keyinggates.
 27. The combination according to claim 23 wherein a first diodeis coupled between each of said key switches and each of said second R-Cattack networks and wherein each of said third keying gates comprisesthe combination of: a second diode coupled to its correspondingisolating gate, a first relatively high resistor between said seconddiode and said output system, a second voltage-dropping resistor betweensaid second R-C attack network and the junction between said seconddiode and said first resistor, a third relatively low resistor shuntedbetween the common return path and the junction between said firstresistor and said output system, said relatively low resistor being ofthe order of two magnitudes lower than said relatively high resistor.28. The combination according to claim 26 wherein each of said firstkeying gates comprises the combination of: a first diode coupled to itscorresponding isolating gate, a first relatively high resistor betweensaid first diode and said first tone color filters, a second relativelylow resistor shunted between a common return path and the junctionbetween said first resistor and said first tone color filter, saidrelatively low resistor being of the order of two magnitudes lower thansaid relatively high resistor, a third voltage-dropping resistor betweensaid first attack network and the junction between said first diode andsaid first resistor, wherein each of said second gates comprises thecombination of: a second diode coupled to its corresponding isolatinggate, a fourth relatively high reSistor in series with said second diodeand said tone color filter, a capacitor shunted between said commonreturn path and the junction between said second diode and said fourthresistor, and a fifth voltage-dropping resistor between saidlast-mentioned junction and said first R-C attack network, wherein athird diode is coupled between said key switch and said second R-Cattack network and wherein each of said third keying gates comprises thecombination of: a fourth diode coupled to its corresponding isolatinggate, a sixth relatively high resistor between said fourth diode andsaid third tone color filter, a seventh voltage-dropping resistorbetween said second R-C attack network and the junction between saidfourth diode and said sixth resistor, an eighth resistor between saidlast-mentioned junction and said common return path, and a ninthrelatively low resistor shunted between the common return path and thejunction between said sixth resistor and said third tone color filter,said ninth relatively-low resistor being of the order of two magnitudeslower than said sixth relatively high resistor.
 29. In an electronicorgan, a source of periodic square wave tone signals which alternatebetween a first and a reference level, a single isolating gate, which isnonconductive of signals when unbiased, connected in cascade with saidsource, a plurality of solid-state electronic keying gates connected inparallel with each other and all connected in series with said singleisolating gate, a single key operated switch for applying DC biasvoltage concurrently through all said gates and through said source to areference point, and different circuits connected between said keyoperated switch and each separate one of said keying gates, one of saiddifferent circuits being responsive to said square wave signals forgenerating correspondingly shaped square waves, and another of saiddifferent circuits being responsive to said square wave signals forgenerating periodic ramp waves, and still another of said differentcircuits including a percussive sustain circuit connected between saidsingle key operated switch and one of said keying gates.
 30. Thecombination according to claim 29 wherein said single isolating gate isa solid-state switch having an output terminal, said solid-state switchpresenting a leakage capacity C in series with said sources, and acapacitor of value nC shunting said output terminal to a referencelevel, where n is of the order of
 100. 31. The combination according toclaim 29 wherein said single isolating gate is a solid-state diodehaving an output terminal, said solid-state diode having a leakagecapacity C in series with said source and a capacitor of value nCshunting said output terminal to a reference level, where n is of theorder of
 100. 32. The combination according to claim 29 wherein all saidgates are solid-state gates.